In /usr/bin/sdl2-config line 19:
  -*=*) optarg=`echo "$1" | sed 's/[-_a-zA-Z0-9]*=//'` ;;
               ^-- SC2006: Use $(...) notation instead of legacy backticked `...`.

Did you mean: 
  -*=*) optarg=$(echo "$1" | sed 's/[-_a-zA-Z0-9]*=//') ;;


In /usr/bin/sdl2-config line 31:
      echo $prefix
           ^-----^ SC2086: Double quote to prevent globbing and word splitting.

Did you mean: 
      echo "$prefix"


In /usr/bin/sdl2-config line 38:
      echo $exec_prefix
           ^----------^ SC2086: Double quote to prevent globbing and word splitting.

Did you mean: 
      echo "$exec_prefix"


In /usr/bin/sdl2-config line 44:
      echo -I${prefix}/include/SDL2   -D_REENTRANT
             ^-------^ SC2086: Double quote to prevent globbing and word splitting.

Did you mean: 
      echo -I"${prefix}"/include/SDL2   -D_REENTRANT

For more information:
  https://www.shellcheck.net/wiki/SC2086 -- Double quote to prevent globbing ...
  https://www.shellcheck.net/wiki/SC2006 -- Use $(...) notation instead of le...